Adhesive composition and thermal transfer sheet

ABSTRACT

The present invention provides an adhesive composition comprising a copolymer (a) of a methylmethacrylate (MMA) and/or a butylmethacrylate (BMA) and a styrene (St), also provides an adhesive composition comprising a mixture of an acrylic polymer (b) and a ketone resin, wherein the acrylic polymer (b) is at least one polymer selected from the group consisting of a poly MMA, a poly BMA, a MMA/BMA copolymer or a MMA/BMA/St copolymer, and also provides a thermal transfer sheet having a layer comprising the adhesive composition. The adhesive composition has excellent heat sealing characteristics and resistance to blocking when it is used for the formation of an adhesive layer, is also superior in miscibility with various organic or inorganic additives and allows these additives to exhibit their functions sufficiently when these additives are added and has high transparency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an adhesive composition and a thermaltransfer sheet, and, more particularly, to an adhesive composition whichhas excellent heat sealing characteristics and resistance to blockingwhen it is used for the formation of an adhesive layer, is also superiorin miscibility with various organic or inorganic additives and allowsthese additives to exhibit their functions sufficiently when theseadditives are added and has high transparency, and also to a thermaltransfer sheet having a layer comprising the adhesive composition.

2. Description of the Related Art

The formation of an image using, for example, a sublimation type thermaltransfer system, melt type thermal transfer system or ink jet system hasbeen of very wide prevalence. These systems can form a beautiful imagesimply and are therefore widely used for printing in a small lot and forpersonal use.

It is known that in an image formed in the above simple image formingsystem, neither a strong binder nor a film forming material is usuallyused unlike the case of general printing systems such as offset printingand gravure printing and the resulting image is therefore inferior infriction resistance, light resistance, weatherability and chemicalresistance. As a method of solving such a problem, a method in which atransparent resin layer is formed as a protect layer on the surface ofan image is used and a simple method of forming a protect layer, forexample, a protect layer thermal transfer system is known.

In the above protect layer transfer system, a transferable transparentresin layer is transferred to and laminated on a desired position of animage by using a protect layer thermal transfer sheet provided with thetransparent resin layer on one surface of a substrate sheet. Such aprotect layer transfer sheet is generally provided with a heat sealingadhesive layer on the surface of a protect layer so that the protectlayer is easily transferred. Further, various additives such as anultraviolet absorber, silica, polyethylene wax, conductive material andantistatic agent are added to the adhesive layer.

SUMMARY OF THE INVENTION

However, the aforementioned conventional adhesive has a poor affinity tovarious additives. For instance, it has inferior compatibility withorganic additives such as an ultraviolet absorber and wax and is alsoinferior in the dispersibility of each inorganic particle, causing theadhesive layer to be turbid occasionally and this often leads todeterioration in the quality of an image to be coated. Moreover, theprotect layer thermal transfer sheet using a conventional adhesive oftengives rise to defects such as blocking owing to an adhesive layerdisposed at a position of the outermost layer. Also, a conventionaladhesive has insufficient adhesive force and there is therefore the casewhere the protect layer is peeled off after the protect layer istransferred.

Accordingly, it is an object of the present invention to provide anadhesive composition which has excellent heat sealing characteristicsand resistance to blocking when it is used for the formation of anadhesive layer, is also superior in miscibility with various organic orinorganic additives and allows these additives to exhibit theirfunctions sufficiently when these additives are added and has hightransparency, and also to provide a thermal transfer sheet having alayer comprising the adhesive composition.

The above object is attained by the present invention shown below.Specifically, the present invention provides an adhesive compositioncomprising a copolymer (a) of a methylmethacrylate (MMA) and/or abutylmethacrylate (BMA) and a styrene (St). The present invention alsoprovides an adhesive composition comprising a mixture of an acrylicpolymer (b) and a ketone resin, wherein the acrylic polymer (b) is atleast one polymer selected from the group consisting of a poly MMA, apoly BMA, a MMA/BMA copolymer or a MMA/BMA/St copolymer. The presentinvention further provides various thermal transfer sheets using theadhesive composition.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a cross sectional view schematically showing one example ofthe protect layer thermal transfer sheet of the present invention;

FIG. 2A is a plane view schematically showing one example of the complexthermal transfer sheet of the present invention; and,

FIG. 2B is a cross sectional view schematically showing the same complexthermal transfer sheet of the FIG. 2A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be explained in more detail by way ofpreferable embodiments.

An adhesive composition of the present invention may contain as anessential adhesive substance, a copolymer (a). The copolymer (a) is oneproduced by polymerizing at least one acrylic monomer selected from thegroup consisting of methylmethacrylate (MMA) and butylmethacrylate (BMA)with styrene (St).

The adhesive composition of the present invention may contain as anessential adhesive substance, an acrylic polymer (b), and when theacrylic polymer (b) is used, a ketone resin is mixed therewith. Theacrylic polymer (b) is at least one polymer or copolymer selected fromthe group consisting of a polymethylmethacrylate, apolybutylmethacrylate, a methylmethacrylate/butylmethacrylate copolymeror a methylmethacrylate/butylmethacrylate/styrene copolymer.

The “ketone resin” in the present invention means a synthetic resinobtained by a reaction of a ketone compound with an aldehyde compoundand includes acetaldehyde resins, acetone furfural resins or the like.These ketone resins may be available from the market and used in thepresent invention.

Embodiments of an adhesive composition according to the presentinvention includes the following structures (wherein “+” means a mixtureand “×” means a copolymer):

“MMA”×“St” copolymer;

“BMA”×“St” copolymer;

“MMA”×“BMA”×“St” copolymer;

“Poly MMA”+“ketone resin”;

“Poly BMA”+“ketone resin”;

“MMA”×“BMA” copolymer+“ketone resin” and

“MMA”×“BMA”×“St” copolymer+“ketone resin”.

In the foregoing embodiments, a preferable ratio by weight of an acrylicresin to a ketone resin is as follows: acrylic resin:ketone resin=25 to30:1 to 5. Also, a preferable ratio by weight of an acrylic monomer to astyrene monomer is as follows: acrylic monomer:styrene monomer=25 to30:1 to 5. The foregoing copolymer (a) or acrylic polymer (b) preferablyhas a glass transition temperature (Tg) of 40° C. to 100° C. and morepreferably 50 to 90° C. and preferably has a weight average molecularweight of 20000 to 150000 and more preferably 25000 to 130000. When theratio of monomers, Tg or weight average molecular weight is out of theabove each defined range, there is the case where unsatisfactoryblocking resistance, adhesion and miscibility with additives areobtained.

The aforementioned copolymer (a) or acrylic polymer (b) used as theadhesive may be produced using usual methods. Examples of these methodsinclude a method in which an appropriate polymerization initiator isadded to the foregoing monomer mixture to carry out solid phasepolymerization and also include solution polymerization carried out in asolvent such as methyl ethyl ketone, toluene or a mixture of thesesolvents, emulsion polymerization carried out by emulsifying a monomerin an aqueous medium and suspension polymerization carried out bysuspending a monomer in an aqueous medium. The polymer solution obtainedby the solution polymerization in the above method or the polymersolution obtained by emulsion polymerization and suspensionpolymerization are advantageous because these solutions can be usedeither as they stand or by adding a ketone resin to form an adhesivelayer.

The solid concentration of the above polymer solution is generally about10 to 40% by weight. This polymer solution contains the copolymer (a) orthe mixture of acrylic polymer (b) and the ketone resin, an essentialadhesive, and it may further contain additives, as required, such asultraviolet absorber, silica, polyethylene wax, conductive material andantistatic agent to the extent that the adhesive does not lose itstransparency.

For example, the polymer solution may contain ultraviolet absorber in anamount of 0.1 to 70 parts by weight, silica in an amount of 0.1 to 15parts by weight, polyethylene wax in an amount of 0.1 to 15 parts byweight, conductive material in an amount of 0.1 to 60 parts by weightand antistatic agent in an amount of 0.1 to 15 parts by weight per 100parts by weight of the essential adhesive.

The adhesive composition of the present invention is useful for variousadhesive applications. The adhesive composition of the present inventionwill be explained taking an example of the composition used for anadhesive layer of a thermal transfer sheet. However, the adhesivecomposition of the present invention is not limited to the followingthermal transfer applications.

(1) Protect Layer Thermal Transfer Sheet

FIG. 1 shows one example of the protect layer thermal transfer sheet. Inthe FIG. 1, the protect layer thermal transfer sheet 101 has a structurein which a protect layer 3 with thickness of about 0.5 to 10 μm made ofa transparent resin such as polyester resin, acrylic resin or the likeis disposed on a substrate film 1 excellent in heat resistance such as apolyester film, as required, via a release layer 2 and further anadhesive layer 4 with thickness of about 0.5 to 10 μm comprising theadhesive composition of the present invention is disposed on the surfaceof the protect layer 3.

In the protect layer thermal transfer sheet 101, a set of the protectlayer 3 and the adhesive layer 4 constitutes a transfer layer 5 which istransferable to a surface of a transfer-receiving material which may beprovided with an image. The adhesive layer 4 constitutes an outermostlayer of the transfer layer. The release layer 2 may be contained in thetransfer layer so as to be transferred together with the other layers,or it may be left on the substrate film 1 at the time of transferprocess.

The protect layer thermal transfer sheet is overlapped on a surface ofan image formed by, for example, a sublimation type thermal transfersystem, ink jet system, electrophotographic system or heat-melt transfersystem or on a surface of an image formed on a card or the like, in suchmanner that the adhesive layer faces the image surface. Then, theprotect layer thermal transfer sheet is heated from the backside thereofby means of a thermal head, heat plate or heat roll to transfer theadhesive layer and the protect layer on the surface of the image therebyimparting various kinds of durability to the image.

At this time, even if various additives are added to the foregoingadhesive layer, the adhesive layer is uniformly transparent andtherefore the quality of the image is not lowered. Also, for formationof the adhesive layer, the copolymer (a) or acrylic polymer (b) having acopolymerization ratio of monomers, Tg and molecular weight each fallingin a specified range is selected and an appropriate amount of a ketoneresin is combined as required, whereby the transferred protect layer isnot peeled off with elapse of time and also, no blocking is caused evenif the protect layer thermal transfer sheet is wound roll-wise.

(2) Receptor Layer Thermal Transfer Sheet

The receptor layer thermal transfer sheet may has a structure similar tothat shown in the FIG. 1 of the protect layer thermal transfer sheet.That is, the receptor layer thermal transfer sheet may has a structurein which a receptor layer comprising a resin receptible a sublimationdye, such as a polyester resin, vinyl chloride/vinyl acetate copolymeror the like, is disposed on a substrate film excellent in heatresistance such as a polyester film, as required, via a release layerand further an adhesive layer with thickness of about 0.5 to 10 μmcomprising the adhesive composition of the present invention is disposedon the surface of the receptor layer. In this case, since the adhesivelayer is not positioned on an image, it is unnecessary for the adhesivelayer to be transparent and therefore a white pigment such as titaniumoxide may be added to the adhesive layer.

The above receptor layer thermal transfer sheet serves to make a regionallowing the formation of an image in a sublimation thermal transfersystem. Specifically, the receptor layer thermal transfer sheet isoverlapped on a desired substrate, such as various kinds of paper,synthetic paper, plastic sheets, metals and woods, which is not dyedwith a sublimation dye, in such manner that the adhesive layer faces thesubstrate, and then it is heated from the backside by means of a thermalhead, heat plate or heat roll, whereby transferring the adhesive layerand the receptor layer. Also, the use of the adhesive composition of thepresent invention ensures that the transferred receptor layer is notpeeled off with elapse of time and also, no blocking is caused even ifthe receptor layer thermal transfer sheet is wound roll-wise.

(3) Adhesive Layer Thermal Transfer Sheet (Application to anIntermediate Transfer System or the Like)

The adhesive layer thermal transfer sheet may has a structure similar tothat shown in the FIG. 1 of the protect layer thermal transfer sheet.That is, the adhesive layer thermal transfer sheet may has a structurein which a transferable adhesive layer with thickness of about 0.5 to 10μm comprising the adhesive composition of the present invention isdisposed on a substrate film excellent in heat resistance such as apolyester film, as required, via a release layer. The adhesive layerthermal transfer sheet may be used for a so-called intermediate transfersystem in which, for example, a desired image is formed on the abovereceptor layer thermal transfer sheet, the adhesive layer is transferredto either the surface of the receptor layer provided with the image or adesired region of an article to which the receptor layer on which theimage is formed is to be transferred and the receptor layer on which theabove image is formed is transferred to the surface of the product bymaking use of the adhesive layer.

Also, the above intermediate transfer system may be a system in which adye receptor layer is disposed on a transparent substrate film, an imageis formed on the receptor layer, the adhesive layer is transferred tothe surface of the receptor layer provided with the image from theaforementioned adhesive layer transfer sheet, the receptor layerincluding the transparent substrate film is applied to the desiredarticle, thereby using the transparent film as a protect layer for theimage.

In the other embodiment, the adhesive layer may be transferredbeforehand from the adhesive layer thermal transfer sheet to a desiredposition of the surface of the transfer-receiving article. Then, the dyereceptor layer is transferred from the receptor layer thermal transfersheet to the surface of the adhesive layer fixed on thetransfer-receiving article. In this embodiment, the dye receptor layerto be transferred may be already provided with the image or no image. Ifthe dye receptor layer has no image, it is transferred from the receptorlayer thermal transfer sheet to the surface of the adhesive layer fixedon the transfer-receiving article, and then the image is formed on thetransferred receptor layer.

In this case, since the adhesive layer is not positioned on an image, itis unnecessary for the adhesive layer to be transparent and therefore awhite pigment such as titanium oxide may be added to the adhesive layer.The use of the adhesive composition of the present invention ensuresthat the transferred receptor layer is not peeled off with elapse oftime and also, no blocking is caused even if the adhesive layer thermaltransfer sheet is wound roll-wise.

Moreover, a protect layer thermal transfer sheet, a receptor layerthermal transfer sheet and an adhesive layer thermal transfer sheet suchas those aforementioned may be respectively made into a complex thermaltransfer sheet having two or more juxtaposed layers.

One example of the complex thermal transfer sheet is schematically shownin FIGS. 2A and 2B, in which the FIG. 2A is a plane view, and the FIG.2B is a cross sectional view. In the FIGS. 2A and 2B, the complexthermal transfer sheet 102 has at least one transfer layer 5 whichcontains the adhesive layer 4 as the outermost layer, any layer selectedamong the transferable protect layer 6, the transferable receptor layer7 and the transferable adhesive layer 8 and the release layer 2, andfurther has at least one colorant layer(9Y, 9M and 9C) intended todesired color such as yellow(9Y), magenta(9M) and cyan(9C), by formingthe transfer layer 5 on a part of a substrate film 1 and further formingone or more colorant layers 9Y, 9M and 9C each comprising a sublimationdye in such manner that each layer is arranged alternately and side byside with each other on the same surface of the substrate film.

The present invention as to various transfer sheets as aforementioned ischaracterized by the use of the adhesive composition of the presentinvention. Other structures, for example, each structure of thesubstrate film, a lubricating heat resistant layer formed on thebackface of the substrate film, the release layer, the protect layer,the receptor layer and the dye layer may be a known structure and noparticular limitation is imposed on these other structures.

The present invention can provide an adhesive composition which hasexcellent heat sealing characteristics and resistance to blocking whenit is used for the formation of an adhesive layer, is also superior inmiscibility with various organic or inorganic additives and allows theseadditives to exhibit their functions sufficiently when these additivesare added and has high transparency, and also provide a thermal transfersheet having a layer comprising the adhesive composition.

EXAMPLES

The present invention will be explained in more detail by way ofexamples and comparative examples, in which all designations of “parts”and “%” indicate parts by weight and weight percentage (wt. %),respectively, unless otherwise noted.

Examples 1 to 3 and Comparative Examples 1 and 2

A monomer composition shown in the following Table 1 was polymerizedusing azobisisobutyronitrile as a porimarization initiator in methylethyl ketone/toluene (weight ratio: 1/1) at 50 to 90° C. for 5 hours anda ketone resin was added as required to obtain an adhesive solution witha solid concentration of 20%. TABLE 1 MONOMER COMPOSITION OF ADHESIVEExample No. & Abbreviation Monomer composition Mw Tg Example 1 H1MMA/BMA/St copolymer 65000 75° C. (weight ratio acrylic:St = 28:2)Example 2 H2 MMA/BMA copolymer + ketone 30000 85° C. resin (weight ratioacrylic:ketone = 28:2) Example 3 H3 MMA/BMA/St copolymer + 50000 80° C.ketone resin (weight ratio acrylic:St:ketone resin = 25:2:3) ComparativeH4 MMA 120000 57° C. Example 1 Comparative H5 MMA + BMA 120000 63° C.Example 2

The weight average molecular weight and Tg of the obtained copolymer (a)or acrylic polymer (b) were measured according to the following methods.

<Method of Measuring the Weight Average Molecular Weight>

The molecular weight of the copolymer (a) or acrylic polymer (b) wasmeasured by GPC (gel permeation chromatography) using tetrahydrofuran asa solvent.

<Method of Measuring Tg>

Tg was measured by a commonly known DSC (differential calorimeter).

<Test for Miscibility of the Adhesive Composition with VariousAdditives>

Additives shown in the following Table 2 were mixed in 100 parts of eachof the adhesive solutions H1 to H5 used in the above examples andcomparative examples. Then, each solution mixed with the additives wasstirred at 30° C. for 60 minutes and then allowed to stand stationarilyfor 60 minutes to prepare adhesive compositions (A to O) according tothe present invention and adhesive compositions (P to Y) of comparativeexamples. The state of each composition was observed visually. Theresults are shown in Table 3. TABLE 2 TYPE OF ADDITIVE Additives &Abbreviation Content Ultraviolet S1 Benzophenone type ultravioletabsorber absorber (UVA635L, manufactured by BASF) Ultraviolet S2Benzotriazole type ultraviolet absorber absorber (TINUVIN900,manufactured by Ciba Geigy) Silica S3 SYLYSIA 310 (manufactured by FujiSilysia Chemical Ltd.) Silica S4 SYLOSPHERE 1504 (manufactured by FujiSilysia Chemical Ltd.) Wax S5 Polyethylene wax (average particle size: 5μm)

TABLE 3 RESULT OF MISCIBILITY TEST Additives Additives S1 S2 S3 S4 S5 H1A ∘ B ∘ C ∘ D ∘ E ∘ (100) (50) (3) (3) (4) H2 F ∘ G ∘ H ∘ I ∘ J ∘ (100)(50) (3) (3) (4) H3 K ∘ L ∘ M ∘ N ∘ O ∘ (100) (50) (3) (3) (4) H4 P x QΔ R x S Δ T Δ (100) (50) (3) (3) (4) H5 U x V Δ W Δ X Δ Y Δ (100) (50)(3) (3) (4)

A to Y in the Table 3 are abbreviations of the adhesive compositions.The values in the parenthesis in the table indicate the amount (parts)of the additive per 100 parts of the adhesive solution.

<Criteria for the Evaluation of Miscibility>

◯: Precipitation, sedimentation and turbidity do not occur.

Δ: Precipitation, sedimentation and turbidity slightly occur.

x: Precipitation, sedimentation and turbidity occur extremely.

As aforementioned, the adhesive compositions (A to O) of the presentinvention do not produce turbidity and have high transparency andstability even if additives are added.

Example 4 and Comparative Example 3

The following layers were laminated on one surface of a polyethyleneterephthalate film (PET) provided with a heat-resistant lubricatingbackface layer to make four protect layer thermal transfer sheets (a) to(d).

(a) PET/release layer/protect layer/adhesive layer

(b) PET/protect layer/adhesive layer

(c) PET/release layer/adhesive layer

(d) PET/adhesive layer

The adhesive layers of the above thermal transfer sheets (c) and (d)function also as a protect layer. The thickness of each layer of theabove protect layer transfer sheets was designed as follows: releaselayer: 0.5 to 3.0 g/m², protect layer: 0.5 to 5.0 g/m² and adhesivelayer: 0.5 to 5.0 g/m² Also, the composition of each layer is asfollows. <Release layer> Silicone modified acrylic resin (Celtop 226, 16parts manufactured by Daicel Chemical Industries, Ltd.) Aluminumcatalyst (Celtop CAT-A, manufactured by 3 parts Daicel ChemicalIndustries, Ltd.) Methyl ethyl ketone 8 parts Toluene 8 parts

<Protect layer> Acrylic resin (Thermolack LP45M, manufactured by Soken50 parts Chemical & Engineering Co., Ltd.) Methyl ethyl ketone 25 partsToluene 25 parts<Adhesive Layer>

Adhesive Compositions A to Y Described in the Aforementioned Table 3

The adhesive compositions A to Y were used in the structures of theabove protect layer thermal transfer sheets (a) to (d) to makeevaluation. As a result, even if any one of the adhesive compositions Ato Y was used in the protect layer thermal transfer sheets (a) to (d),the protect layer was transferred without any problem. However, in thecase of the protect layer (adhesive layer) transferred from the protectlayer thermal transfer sheets using the adhesive compositions P to Yrespectively in the comparative examples, a reduction in transparency(haze) and surface roughness were caused by inferior miscibility of theadhesive composition with the result that the visualization of an imageunder the protect layer was hindered. On the other hand, no problemarose at all concerning the visualization of an image under the protectlayer transferred from the protect layer thermal transfer sheet producedusing the adhesive compositions A to O of the present invention.

Example 5 and Comparative Example 4

The following layers were laminated on one surface of a polyethyleneterephthalate film (PET) provided with a heat-resistant lubricatingbackface layer to make two receptor layer thermal transfer sheets (a)and (b).

(a) PET/release layer/receptor layer/adhesive layer

(b) PET/receptor layer/adhesive layer

The thickness of each layer of the above receptor layer transfer sheetswas designed as follows: release layer: 0.5 to 3.0 g/m², receptor layer:0.5 to 5.0 g/m² and adhesive layer: 0.5 to 5.0 g/m². Also, thecompositions of the release layer and adhesive layer are the same asthose of the above Example 4 and the composition of the receptor layeris as follows. <Receptor layer> Vinyl chloride/vinyl acetate copolymerresin (1000 ALK, 100 parts manufactured by Denka Vinyl) Epoxy modifiedsilicone (X-22-3000T, manufactured by 10 parts Shin-Etsu Chemical Co.,Ltd.) Methyl ethyl ketone 10 parts Toluene 25 parts

The adhesive compositions A to Y were used in the structures of theabove receptor layer thermal transfer sheets (a) and (b) to makeevaluation. As a result, in the case of those obtained by using theadhesive compositions A to Y in each structure of the receptor layerthermal transfer sheets (a) and (b), the receptor layer was transferredwithout any problem. However, in the case of transfer of the receptorlayer by using the receptor layer thermal transfer sheets using theadhesive compositions P to Y respectively in the comparative examples, areduction in the transparency and surface roughness were caused byinferior miscibility of the adhesive composition with the result thathaze and appearance inferior due to lines were caused on the imageformed on the receptor layer, so that the outward appearance wasimpaired. On the other hand, no problem arose at all concerning theformation of an image on the receptor layer transferred when using thereceptor layer transfer sheets using the adhesive compositions A to O ofthe present invention respectively.

Example 6 and Comparative Example 5

A full-color image was formed using a sublimation thermal transfersystem on the same receptor layer thermal transfer sheet a′ which is thesame as that of Example 5 except that no adhesive layer was formed. Thenthe adhesive layer was transferred from the thermal transfer sheet (c)of Example 4 to the surface on which the image was formed. This imagewas retransferred to the surface of a desired transfer-receivingmaterial by means of a laminator.

As a result, even if anyone of the adhesive compositions A to Y was usedfor the formation of the adhesive layer, the image was retransferredwithout any problem. However, in the case of using the adhesivecompositions P to Y respectively in the comparative examples, areduction in the transparency and surface roughness were caused byinferior miscibility of the adhesive composition with the result thathaze and appearance inferior due to lines were caused under thetransferred image, so that the outward appearance was impaired. On theother hand, neither haze nor lines was observed in the case of using theadhesive compositions A to O of the present invention respectively andno problem arose concerning image qualities.

1. An adhesive composition comprising a copolymer (a) of a methylmethacrylate and/or a butylmethacrylate and a styrene.
 2. An adhesive composition according to claim 1, wherein Tg of the copolymer (a) or acrylic polymer (b) is 40° C. to 100° C. and the weight average molecular weight of the polymer or copolymer is 20000 to
 150000. 3. An adhesive composition according to claim 1, the composition comprising at least one additive selected from the group consisting of a ultraviolet absorber, silica, polyethylene wax, a conductive material and an antistatic agent.
 4. An adhesive composition comprising a mixture of an acrylic polymer (b) and a ketone resin, wherein the acrylic polymer is at least one polymer or copolymer selected from the group consisting of polymethylmethacrylate, polybutylmethacrylate, methylmethacrylate/butylmethacrylate copolymer or methylmethacrylate/butylmethacrylate/styrene copolymer.
 5. An adhesive composition according to claim 4, wherein Tg of the copolymer (a) or acrylic polymer (b) is 40° C. to 100° C. and the weight average molecular weight of the polymer or copolymer is 20000 to
 150000. 6. An adhesive composition according to claims 4, the composition comprising at least one additive selected from the group consisting of a ultraviolet absorber, silica, polyethylene wax, a conductive material and an antistatic agent.
 7. A thermal transfer sheet comprising a transfer layer disposed in a peelable manner on at least a part of one surface of a substrate sheet, wherein the transfer layer contains a layer consisting of the adhesive composition which comprises a copolymer (a) of a methylmethacrylate and/or a butylmethacrylate and a styrene at a position of an outermost layer.
 8. A thermal transfer sheet according to claim 7, wherein the sheet further comprises a release layer between the substrate sheet and the adhesive layer.
 9. A thermal transfer sheet according to claim 7, wherein the sheet further comprises a transferable protect layer or a transferable receptor layer between the substrate sheet and the adhesive layer.
 10. A thermal transfer sheet according to claim 9, wherein the sheet further comprises a release layer between the substrate sheet and the transferable protect layer or the transferable receptor layer.
 11. A thermal transfer sheet according to claim 7, the sheet further comprises a colorant layer provided alternately and side by side with the transfer layer.
 12. A thermal transfer sheet comprising a transfer layer disposed in a peelable manner on at least a part of one surface of a substrate sheet, wherein the transfer layer contains a layer consisting of the adhesive composition which comprises a mixture of an acrylic polymer (b) and a ketone resin, the acrylic polymer being at least one polymer or copolymer selected from the group consisting of polymethylmethacrylate, polybutylmethacrylate, methylmethacrylate/butylmethacrylate copolymer or methylmethacrylate/butylmethacrylate/styrene copolymer.
 13. A thermal transfer sheet according to claim 12, wherein the sheet further comprises a release layer between the substrate sheet and the adhesive layer.
 14. A thermal transfer sheet according to claim 12, wherein the sheet further comprises a transferable protect layer or a transferable receptor layer between the substrate sheet and the adhesive layer.
 15. A thermal transfer sheet according to claim 14, wherein the sheet further comprises a release layer between the substrate sheet and the transferable protect layer or the transferable receptor layer.
 16. A thermal transfer sheet according to claim 12, the sheet further comprises a colorant layer provided alternately and side by side with the transfer layer. 